In general, circuitry is manufactured on hard printed circuit boards or flexible substrates. Printed circuit boards include materials like epoxy-resin or epoxy-glass boards. One generic class on which these circuits are manufactured is FR4. Alternatively flexible substrates, also called "flex", include structures of copper on polyimide. These circuits are generally used in automobiles, consumer electronics, and general interconnections.
A well known technology for attaching semiconductor circuits, or "chips" to the circuit board or flex structures is called wirebonding. Wire bonds are made from small diameter wires in the range of 25 microns in diameter and are very short. Generally the wire bonds are on the order of 1 millimeter (mm) in length. These wire bonds are normally kept short for several reasons:
1. The small diameter of the wire makes it very weak. PA1 2. In typical circuits many bonds are made and longer lengths would make the connections more prone to electrical shorting. PA1 3. Longer lengths of the wires increase self and mutual inductance which degrade the electrical performance of the circuit.
Radio Frequency Identification (RF ID) is just one of many identification technologies for identifying objects. The heart of the RF ID system lies in an information carrying tag. The tag functions in response to a coded RF signal received from a base station. The tag reflects the incident RF carrier back to the base station. Information is transferred as the reflected signal is modulated by the tag according to its programmed information protocol.
The tag consists of a semiconductor chip having RF circuits, logic, and memory. The tag also has an antenna, often a collection of discrete components, capacitors and diodes, for example, a battery in the case of active tags, a substrate for mounting the components, interconnections between components, and a means of physical enclosure. One variety of tag, passive tags, has no battery. They derive their energy from the RF signal used to interrogate the tag. In general, RF ID tags are manufactured by mounting the individual elements to a circuit card. This is done by using either short wire bond connections or soldered connections between the board and the circuit elements: chip, capacitors, diodes, antenna. The circuit card may be of epoxy-fiberglass composition or ceramic. The antennas are generally loops of wire soldered to the circuit card or consist of metal etched or plated on a circuit card. The whole assembly may be enclosed in a plastic box or molded into a three dimensional plastic package.
While the application of RF ID technology is not as widespread as other ID technologies, barcode for example, RF ID is on its way to becoming a pervasive technology in some areas, notably vehicle identification.
Growth in RF ID has been inhibited by the absence of infrastructure for manufacturing the tags, the high cost of tags, the bulkiness of most of the tags, problems of tag sensitivity and range, and the need for the simultaneous reading of multiple numbers of tags. A typical tag costs in the $5 to $10 range. Companies have focused on niche applications. Some prior art is used to identify railway boxcars. RF tags are now used in the automatic toll industry, e.g. on thruway and bridge tolls. RF tags are being tested for uses as contactless fare cards for buses. Employee identification badges and security badges have been produced. Animal identification tags are also commercially available as are RF ID systems for tracking components in manufacturing processes.
One limitation of making RF tags made from PC boards or flex is that the flex or boards must be manufactured first. For very high volumes of tags (greater than one hundred million tags) new factories must be built to accommodate the capacity needed for board or flex production to meet tag demand. Further, RF tags made from these technologies are too expensive for many applications. For example, bar codes are a technology that is used for identification at a much lower cost than existing RF tagging technology.